Until now, Quaternary paleoecologists have regarded evolution as a slow process relative to climate change, predicting that the primary biotic response to changing climate is not adaptation, but instead (1) persistence in situ if changing climate remains within the species tolerance limit, (2) range shifts (migration) to regions where climate is currently within the species' tolerance limits, or (3) extinction. We argue here that all three of these outcomes involve evolutionary processes. Genetic differentiation within species is ubiquitous, commonly via adaptation of populations to differing environmental conditions...Collaboration between paleoecologists and evolutionary biologists can refine interpretations of paleo-records, and improve predictions of biotic response to anticipated climate change.

We sought to understand differences in tree response to meteorological drought among species and soil types at two ecotone forests in northern Arizona, the pinyon-juniper woodland/ponderosa pine ecotone, and the higher elevation, wetter, ponderosa pine/mixed conifer ecotone...Our findings of different responses to drought among co-occuring tree species and between low and high elevation populations are interpreted in the context of drought impacts on montane coniferous forests of the southwestern USA.

Concentrations of the greenhouse gases CO2, CH4 and N2O are increasing in the atmosphere, and evidence suggests that this is already causing significant changes in the Earth’s climate. Results from numerous investigations indicate that increased atmospheric CO2 often leads to increased plant production, greater water use efficiency and higher soil water content, but may also result in reduced forage quality, with consequent lowered digestibility, particularly in nutrient-limited systems. Predicted future increases in temperature will have varied effects on plants and animals through alterations in growing season length, metabolism, energy dynamics and system water relations. The potential for increased plant productivity due to CO2 fertilization as temperatures increase will often be greater in present-day mesic, temperate and cold ecosystems, but may be offset to the extent temperatures increase and conditions become more desiccating in world regions that are predicted to become more drought prone. Rainfall is predicted to increase in some areas, but may not result in more production in cases where increased storm intensity will lead to more runoff and erosion. These basic responses will be modulated by changes in plant and animal species composition that result from competitive species interactions in native ecosystem responses to global climate change, or are the consequence of management strategies to select better adapted plant and animal species or genotypes. Management options for adapting to global climate change are discussed for intensively managed improved pastures as well as for native rangelands.

There is significant uncertainty about the effects of global change on the vegetation and animal productivity of pasture and rangeland ecosystems. This paper presents a synthesis of progress made between 1994 and 1999 in the Global Change and Terrestrial Ecosystems (GCTE) Pastures and Rangelands Core Research Project 1 (CRP1) network, a world-wide network of 83 full-time equivalent researchers established in different pasture and rangelands systems to reduce these uncertainties. The network focuses on key processes controlling forage and animal production at a paddock/landscape scale, in order to improve the ability to model animal production. To date, the network has resulted in a considerable reduction in the uncertainties about the effects of elevated CO2 on growth, and to a lesser extent composition and forage quality, of intensive pastures in cool, wet climatic zones. However, knowledge of other grazed ecosystems and processes is more limited. The greatest confidence is in predicting implications for vegetation production, with lesser confidence in implications for vegetation composition, animal production and adaptation options. Overall, the stimulatory effect of double ambient CO2 on grassland production averages about C17% in ecosystem-based experiments. This is less than previous estimates. Individual system responses to elevated CO2 can vary widely and are predicted to be higher in moisture-limited and warm-season grassland systems. Species composition change is likely to be an important mechanism altering grassland production and its value for grazing livestock, especially in drier rangelands with woody shrub invasion. On average, the legume content of productive grass–legume swards is increased by C10% due to CO2 enrichment. Leaf nitrogen reductions due to elevated CO2 are often observed but are generally modest compared with effects of other management factors. New data collection efforts should be focused in areas of the world which are most sensitive to food security issues and most subject to global change, in particular humid semi-arid margins and subtropical grasslands. There remains no good basis for extrapolating findings between different pasture and rangeland systems. This synthesis indicates that greater focus is required on the linkages between the biophysical, social and economic factors that will influence future changes in pasture and rangeland ecosystems and their implications for food Security

Abstract Rapidly expanding insect populations, deforestation and global climate change threaten to destabilize key planetary carbon pools, especially the Earth's forests, which link the micro-ecology of insect infestation to climate. To the extent mean temperature increases, insect populations accelerate deforestation. This alters climate via the loss of active carbon sequestration by live trees and increased carbon release from decomposing dead trees. A self-sustaining positive feedback loop can then emerge. Extensive field recordings demonstrate that bioacoustic communication plays a role in infestation dynamics and is likely to be a critical link in the feedback loop. These results open the way to novel detection and monitoring strategies and nontoxic control interventions. http://www.mitpressjournals.org/doi/abs/10.1162/leon.2009.42.3.239

Possible Implications of Increased Carbon Dioxide Levels and Climate Change for Desert Ecosystems E. Lioubimtseva1 and J. M. Adams2 (1) Geography and Planning Department, Grand Valley State University, Allendale, Michigan 49401, USA (2) Earth and Environmental Sciences Department, Wesleyan University, Middletown, Connecticut 06459, USA Published online: 23 January 2004 Abstract Despite the considerable progress achieved during recent years in quantifying and modeling climatic and ecological processes caused by increasing concentrations of greenhouse gases in the atmosphere, there are still major uncertainties regarding the potential effects of increasing concentrations of either CO2 (carbon dioxide) or future climate change in arid ecosystems. General Circulation Models predict varying patterns of moister or drier conditions in deserts for the next century, but the results of climatic and ecosystem modeling in relation to deserts in a future greenhouse effect climate are complex and contradictory. Nevertheless, if deserts do respond more dramatically to global temperature change, as they did during the Holocene and, especially the last interglacial era (130,000 years ago), they might act as globally significant sinks of carbon into soils and vegetation. Some growth chamber experiments have indicated that increased CO2 will significantly affect desert shrubs, whereas other chamber and field experiments suggest that rising levels of atmospheric CO2 may not dramatically affect desert ecosystems, although certain individual species may be strongly favored. It is difficult to make a firm statement whether there are any valid analogs between the climate changes of the past and future climate change induced by greenhouse gases. http://www.springerlink.com/content/v11449g8ek3byvyl/

Climatic and Human Influences on Fire Regimes of the Southern San Juan Mountains, Colorado, USA • Author(s): Henri D. Grissino-Mayer, William H. Romme, M. Lisa Floyd and David D. Hanna • Source: Ecology, Vol. 85, No. 6 (Jun., 2004), pp. 1708-1724 • Published by: Ecological Society of America • Stable URL: http://www.jstor.org/stable/3450595 Abstract Fire severity, frequency, and extent are expected to change dramatically in coming decades in response to changing climatic conditions, superimposed on the adverse cumulative effects of various human-related disturbances on ecosystems during the past 100 years or more. To better gauge these expected changes, knowledge of climatic and human influences on past fire regimes is essential. We characterized the temporal and spatial properties of fire regimes in ponderosa pine forests of the southern San Juan Mountains of southwestern Colorado by collecting 175 fire-scarred tree samples from nine sites across a wide range of topographic settings. All tree rings and fire scars were dated using standard dendrochronological techniques. Fire-free intervals were statistically modeled using the Weibull distribution to provide quantitative measures that characterized the historical range of variation in pre-EuroAmerican fire regimes. Fires during our reference period were more frequent in the low elevation ponderosa pine forests (6-10 yr) than in the high elevation, mixed conifer forests (18-28 yr). Fires at lower elevations were predominantly low-severity, isolated fires. Fires during some years (e.g., 1748) were spatially extensive throughout the entire mountain range. Intervals that delimited significantly long fire-free periods ranged from 10-19 yr (low elevation) to 27-50 yr (high elevation). Fire histories were similar between the eastern and western portions of the mountain range, although we found significant evidence of topographic isolation on fire regimes at one site. Pre-1880 fires primarily occurred in the dormant season, and we found no temporal changes in past fire seasonality. We found no compelling evidence that Native Americans influenced fire regimes in our study sites. We found a hiatus in fire occurrence between 1750 and 1770 that we believe was likely related to weakened El Niño-Southern Oscillation activity, an extended series of cool-phase Pacific Decadal Oscillation events, and weakened monsoonal moisture, all possibly entrained in an invasive air mass typical of locations that are more northerly. In addition, pre-1880 fires occurred during years of severe drought, conditioned by above average moisture conditions in preceding years. The 20th century is characterized by a near complete absence of fires (fire-free interval of >100 yr), suggesting future wildfires may be more widespread and ecologically severe compared to pre-1880 fires. http://www.esajournals.org/doi/abs/10.1890/02-0425

Niklas S. Christensen1, Andrew W. Wood1, Nathalie Voisin1, Dennis P. Lettenmaier1 and Richard N. Palmer1 (1) Department of Civil and Environmental Engineering, University of Washington, 164 Wilcox Hall, P.O. Box 352700, Seattle, WA, 98195-2700, U.S.A Abstract The potential effects of climate change on the hydrology and water resources of the Colorado River basin are assessed by comparing simulated hydrologic and water resources scenarios derived from downscaled climate simulations of the U.S. Department of Energy/National Center for Atmospheric Research Parallel Climate Model (PCM) to scenarios driven by observed historical (1950–1999) climate. PCM climate scenarios include an ensemble of three 105-year future climate simulations based on projected `business-as-usual'(BAU) greenhouse gas emissions and a control climate simulation based on static 1995 greenhouse gas concentrations. Downscaled transient temperature and precipitation sequences were extracted from PCM simulations, and were used to drive the Variable Infiltration Capacity (VIC) macroscale hydrology model to produce corresponding streamflow sequences. Results for the BAU scenarios were summarized into Periods 1, 2, and 3 (2010–2039,2040–2069, 2070–2098). Average annual temperature changes for the Colorado Riverbasin were 0.5 °C warmer for control climate, and 1.0, 1.7, and 2.4 °C warmer for Periods 1–3, respectively, relative to the historicalclimate. Basin-average annual precipitation for the control climate was slightly(1%) less than for observed historical climate, and 3, 6, and 3%less for future Periods 1–3, respectively. Annual runoff in the controlrun was about 10% lower than for simulated historical conditions, and 14, 18, and 17% less for Periods 1–3, respectively. Analysis of watermanagement operations using a water management model driven by simulated streamflows showed that streamflows associated with control and future BAU climates would significantly degrade the performance of the water resourcessystem relative to historical conditions, with average total basin storage reduced by 7% for the control climate and 36, 32 and 40% for Periods 1–3, respectively. Releases from Glen Canyon Dam to the LowerBasin (mandated by the Colorado River Compact) were met in 80% of years for the control climate simulation (versus 92% in the historical climate simulation), and only in 59–75% of years for the future climate runs. Annual hydropower output was also significantly reduced for the control and future climate simulations. The high sensitivity of reservoir system performance for future climate is a reflection of the fragile equilibrium that now exists in operation of the system, with system demands only slightly less than long-term mean annual inflow.

Drought-induced shift of a forest–woodland ecotone: Rapid landscape response to climate variation 1. Craig D. Allen*,† and 2. David D. Breshears‡ Abstract In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change. http://www.pnas.org/content/95/25/14839.full

Modelling bark beetle disturbances in a large scale forest scenario model to assess climate change impacts and evaluate adaptive management strategies Rupert Seidl1, 2 , Mart-Jan Schelhaas3, Marcus Lindner1 and Manfred J. Lexer2 Received: 27 May 2008 Accepted: 11 September 2008 Published online: 2 October 2008 Abstract To study potential consequences of climate-induced changes in the biotic disturbance regime at regional to national scale we integrated a model of Ips typographus (L. Scol. Col.) damages into the large-scale forest scenario model EFISCEN. A two-stage multivariate statistical meta-model was used to upscale stand level damages by bark beetles as simulated in the hybrid forest patch model PICUS v1.41. Comparing EFISCEN simulations including the new bark beetle disturbance module against a 15-year damage time series for Austria showed good agreement at province level (R² between 0.496 and 0.802). A scenario analysis of climate change impacts on bark beetle-induced damages in Austria’s Norway spruce [Picea abies (L.) Karst.] forests resulted in a strong increase in damages (from 1.33 Mm³ a−1, period 1990–2004, to 4.46 Mm³ a−1, period 2095–2099). Studying two adaptive management strategies (species change) revealed a considerable time-lag between the start of adaptation measures and a decrease in simulated damages by bark beetles. http://www.springerlink.com/content/m34g774707721385/

Received 28 July 2003; Revised 19 October 2003; accepted 6 November 2003. Available online 19 December 2003.

Abstract This study, using the panel data modeling approach, investigates the relationships between climatic variables and southern pine beetle (SPB) (Dendroctonus frontalis Zimmermann) infestations and assesses the impact of global climate change on SPB infestation risk and damage. The panel data model alleviates possible collinearity among climatic variables, accounts for the effect of omitted or unobserved variables, and incorporates natural and human adaptation, thus representing a more robust approach to analyzing climate change impacts. SPB outbreaks in Louisiana and Texas appeared to move together; infestations in Alabama, Arkansas, Georgia, Florida, Mississippi, South Carolina, North Carolina, and Tennessee were highly correlated; and Virginia demonstrated its unique temporal pattern of SPB outbreaks. Salvage harvest was found to be helpful in lessening future infestation risk. Warmer winters and springs would positively contribute to SPB outbreaks with spring temperature showing a more severe and persistent impact than winter temperature; increases in fall temperature would ease SPB outbreaks; and summer temperature would have a mixed impact on SPB infestations. Compared to temperature, precipitation would have a much smaller impact on SPB infestations. While increases in the previous winter, spring, and fall precipitation would enhance SPB outbreak risk in the current year, a wetter summer would reduce infestations 3 years later. Global climate change induced by doubling atmospheric CO2 concentration would intensify SPB infestation risk by 2.5–5 times. If the changes in the area and productivity of southern pine forests due to climate change are accounted for, SPB would cause even more severe damage, 4–7.5 times higher than the current value of trees killed annually. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T6X-4B8BC42-2&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=ed1dd3e57402b6ebb3047d2145da5b80

Global climate change: the effects on birds in Arizona and the southwest (Jack F)

Just as the canary in the mind shaft warns against change in environmental conditions, birds show early signs in responding to global climate change. Migrating birds are changing habits to compensate for higher global temperatures, by moving north every year. Still many birds are arriving at their summer home and missing the hatching of bugs and blooming of many plants. This slight off set could have drastic effects on the greater ecosystem. Here in the south west where temperature is expected to rise with decreased precipitation, local bird species and migrating bird species could be drastically affected in their life style.

Abstract: The endangered bonytail Gila elegans, a large-bodied, main-stem cyprinid endemic to the Colorado River Basin of the American Southwest, was once widespread and abundant in warm-water-stream reaches. Negative effects of altered flow and temperature regimes downstream of dams, other habitat changes, and establishment of nonnative fishes have reduced populations of native fish throughout the basin, and wild bonytails may be extirpated. Hatchery reared bonytails are stocked in formerly occupied habitat to rebuild depleted populations, but their ecology is poorly understood. In 2002–2007, sampling in the middle Green River from upstream and downstream of stocking locations in Dinosaur National Monument documented survival of bonytails for ≤4 months, but apparently none survived longer. Many fish at large ≤4 months had Lernea or fungal infections, weighed an average of 20% less than fish when released, and had relatively low rates of growth. Post-stocking rates of dispersal downstream (ca. 1 river km/day) were considerable, and potentially, biologically significant. Bonytails occupied pools, eddies, runs, backwaters, and riffles, and co-occurred in eddies with the roundtail chub Gila robusta and humpback chub Gila cypha in Whirlpool Canyon. We also documented two instances of predation by smallmouth bass Micropterus dolomieu on bonytails ≤225 mm in total length. Reduced predation by large-bodied, nonnative, piscivores and increased resistance to disease and other stressors that reduce body condition may increase survival of stocked bonytails in this portion of the Green River. Alternative stocking strategies, including use of alluvial and floodplain areas, and effects of size on survival, are being evaluated.

Abstract: Because of its relatively natural hydrograph, the Yampa River, Colorado, is considered the crown jewel of native fish habitat in the upper basin of the Colorado River and has supported a relatively intact native fish assemblage. Nonnative fishes are thought to pose the greatest threat to native fishes in this system. Removal programs for nonnative northern pike Esox lucius and channel catfish Ictalurus punctatus have highlighted managers' perception of the threat posed by each species. Recent expansion of nonnative smallmouth bass Micropterus dolomieu in the Yampa River attracted an avid angling clientele but also coincided with a precipitous decline in native fishes, necessitating a rigorous assessment of the relative impact of all three nonnative predators on the native fishes. We used abundance, growth, and diet estimates for each predator species to quantify consumptive demand using bioenergetics models. Despite a low abundance of small-bodied fishes and thus a low number of fish in the smallmouth bass diet, total fish consumption by smallmouth bass (mean = 15.2 kg•km−1•year−1; 95% confidence interval [CI] = 13.3–17.1 kg•km−1•year−1) was similar to that estimated for northern pike (mean = 13.7 kg•km−1•year−1, 95% CI = 11.4–16.0 kg•km−1•year−1) and was about 65 times higher than the estimate for channel catfish (mean = 0.22 kg•km−1•year−1; 95% CI = 0.05–0.40 kg•km−1•year−1). Diet data from the upper Colorado River, where small-bodied fish were plentiful, suggested that piscivory by smallmouth bass in the Yampa River could be 10 times the piscivory by northern pike and channel catfish, or about 168.5 kg•km−1•year−1 (95% CI = 147.0–189.9 kg•km−1•year−1), if prey fish were more available. This level of piscivory suggested that smallmouth bass presented the greatest predatory threat to native fishes of the Yampa River. As environmental conditions change, use of field monitoring together with bioenergetics modeling will be an effective framework to assist managers in adapting their nonnative fish control efforts to maximize the likelihood of native fish recovery.

1. Abstract: We investigated the effects of winter and summer drought on a shrub/grass community of the Colorado Plateau in western North America, a winter-cold, summer-hot desert that receives both winter and summer precipitation. Summer, winter and yearlong drought treatments were imposed for 2 consecutive years using rainout shelters. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Growth for all three species was far more sensitive to winter than to summer drought. The primary reason was that plants did not grow in summer and also did not appear to use summer-assimilated carbon to support growth in the following spring. We hypothesize that the relative scarcity and uncertainty of summer rain on the Colorado Plateau prevents most species from evolving adaptations that would improve their use of summer rain. Together with the results of the companion paper, which focused on plant water relations, we conclude that variation in fall to spring precipitation would have strong effects on primary productivity, and could cause reversible fluctuations in community composition, while increased variation in summer precipitation, through causing high rates of mortality among shallow-rooted species in dry years, has the potential to cause lasting and perhaps irreversible community change, especially if coinciding with the invasion of western landscapes by cheatgrass, tumble weed and other grazing tolerant exotics. [Copyright 2005 Elsevier]

2. Abstract: The Colorado Plateau is located in the interior, dry end of two moisture trajectories coming from opposite directions, which have made this region a target for unusual climate fluctuations. A multidecadal drought event some 850 years ago may have eliminated maize cultivation by the first human settlers of the Colorado Plateau, the Fremont and Anasazi people, and contributed to the abandonment of their settlements. Even today, ranching and farming are vulnerable to drought and struggle to persist. The recent use of the Colorado Plateau primarily as rangeland has made this region less tolerant to drought due to unprecedented levels of surface disturbances that destroy biological crusts, reduce soil carbon and nitrogen stocks, and increase rates of soil erosion. The most recent drought of 2002 demonstrated the vulnerability of the Colorado Plateau in its currently depleted state and the associated costs to the local economies. New climate predictions for the southwestern United States include the possibility of a long-term shift to warmer, more arid conditions, punctuated by megadroughts not seen since medieval times. It remains to be seen whether the present-day extractive industries, aided by external subsidies, can persist in a climate regime that apparently exceeded the adaptive capacities of the Colorado Plateau's prehistoric agriculturalists. [ABSTRACT FROM AUTHOR]

We contrasted the seasonal use of simulated large rain events (24 mm) by three native species of the arid Colorado Plateau: the perennial grass Hilaria jamesii and two shrubs Artemesia filifolia and Coleogyne ramosissima. Deuterium-enriched water was used to distinguish shallow "pulse" water from water in deeper soil layers that were unaffected by the water input. We also measured the leaf gas exchange rates of watered and unwatered control plants for 5 days after the rain event. H. jamesii had twice the pulse water proportion in its xylem than the two shrubs in spring (approx. 70% vs 35%). In summer, the pulse water proportions of all species were around 70%. The increase in the relative pulse water uptake of the two shrubs was caused primarily by a reduction in the rate of water uptake from deeper sources, consistent with the decrease in the availability of stored winter water. Rain increased the rates of gas exchange in C. ramosissima in both seasons, in H. jamesii only in summer and had no significant effect on A. filifolia. In H. jamesii, summer rain also increased water use efficiency. This suggests three principle mechanisms for rainwater use: (1) immediate increase in gas exchange via stomatal opening (C. ramisissima), (2) immediate increase in water use efficiency through restoration of the photosynthetic apparatus (H. jamesii) and (3) conservation of deeper soil water, potentially extending photosynthetic activity into later drought periods (A. filifolia). On a ground-area basis, A. filifolia was by far the largest consumer of spring and summer rain, due to its greater ground cover, while rain use by H. jamesii was negligible. We hypothesize that a population's fraction of the total community Leaf Area Index, more than species identity, determines which species takes up most of the spring and summer precipitation and we discuss this idea in the context of Walter and Stadelmann's (1974, In: Brown JW Jr (ed) Desert biology. Academic Press, New York, pp 213-310) water partitioning hypothesis.

Abstract South-eastern Utah forms a northern border for the region currently influenced by the Arizona monosoonal system, which feeds moisture and summer precipitation into western North America. One major consequence predicted by global climate change scenarios is an intensification of monosoonal (summer) precipitation in the aridland areas of the western United States. We examined the capacity of dominant perennial shrubs in a Colorado Plateau cold desert ecosystem of southern Utah, United States, to use summer moisture inputs. We simulated increases of 25 and 50 mm summer rain events on Atriplex canescens, Artemisia filifolia, Chrysothamnus nauseosus, Coleogyne ramosissima, and Vanclevea stylosa, in July and September with an isotopically enriched water (enriched in deuterium but not 18O). The uptake of this artificial water source was estimated by analyzing hydrogen and oxygen isotope ratios of stem water. The predawn and midday xylem water potentials and foliar carbon isotope discrimination were measured to estimate changes in water status and water-use efficiency. At. canescens and Ch. nauseosus showed little if any uptake of summer rains in either July or September. The predawn and midday xylem water potentials for control and treatment plants of these two species were not significantly different from each other. For A. filifolia and V. stylosa, up to 50% of xylem water was from the simulated summer rain, but the predawn and midday xylem water potentials were not significantly affected by the additional summer moisture input. In contrast, C. ramosissima showed significant uptake of the simulated summer rain (>50% of xylem water was from the artificial summer rain) and an increase in both predawn and midday water potentials. The percent uptake of simulated summer rain was greater when those rains were applied in September than in July, implying that high soil temperature in midsummer may in some way inhibit water uptake. Foliar carbon isotope discrimination increased significantly in the three shrubs taking up simulated summer rain, but pre-treatment differences in the absolute discrimination values were maintained among species. The ecological implications of our results are discussed in terms of the dynamics of this desert community in response to changes in the frequency and dependability of summer rains that might be associated with a northward shift in the Arizona monsoon boundary.

http://arizona.sierraclub.org/conservation/grandcanyon/climatechangeGCR.asp Scientists say the Western U.S. will experience the effects of climate change sooner and more intensely than most other regions of the country. The region’s national parks are among the places where the changes in the natural environment will be most evident. As a result, climate change is the single greatest threat to face western national parks, including the Grand Canyon.

http://geochange.er.usgs.gov/sw/impacts/geology/sand/ The biggest impacts of active sand dunes in the region would be on the Navajo and Hopi people, whose reservation land is either on, or downwind of, the largest areas of sand dunes. Many Navajo and Hopi homes are on or near sand dunes; reactivation of dunes would obviously have a negative effect on living conditions. Sheep and cattle are important to the economy of the Navajo and Hopi, and much of the vegetation required for grazing is dune vegetation. In addition, dry farming is practiced in much of the area, some of it on sand dunes. Thus, reactivation of sand dunes in the area would have serious impacts on living conditions, grazing, and farming.

The scarcity of water on the Colorado Plateau can be attributed to a number of different factors. Because it is essentially an arid and semi-arid plateau, water is the most important natural resource. As climate change continues to have an impact of the Colorado Plateau, new strategies must be considered for conserving water. In the past, farmers on the plateau planted cottonwoods and willows at the edge of their fields to reduce moisture stress. Drier, hotter years on the plateau as a result of global warming will lead to an increasing number of wildfires. If warming trends continue, reservoirs all across the plateau will experience more rapid evaporation, as is the case with Lake Powell. Invasive plant species like tamarisk and Russian olive have decimated springs all across the plateau. The Hopi believe that the disappearance of springs is a warning of future environmental problems. This belief seems plausible considering the growing evidence of climate change taking place on the Colorado Plateau.

We investigated the effects of winter and summer drought on plants of the Colorado Plateau in western North America. This winter-cold, summer-hot desert region receives both winter and summer precipitation. Droughts were imposed for two consecutive years using rainout shelters. Here, we examine drought effects on the hydrologic interactions between plants and soil. We chose three perennial species for this study, representing different rooting patterns and responsiveness to precipitation pulses: Oryzopsis hymenoides, a perennial bunch grass with shallow roots; Gutierrezia sarothrae, a subshrub with dimorphic roots; and Ceratoides lanata, a predominantly deep-rooted woody shrub. Drought effects on plant water status were qualitatively similar among species, despite morphological differences. Summer drought affected the water status of all species more negatively than winter drought. Isotopic analysis of stem water revealed that all three species took up deeper soil water under drought conditions and shallow soil water after a large rainfall event in summer. Thus all three species appeared to use the same water sources most of the time. However, after a particularly dry summer, only the deepest-rooted species continued to take up soil water, while the more shallow-rooted species were either dead or dormant. Our study suggests therefore that increased occurrence of summer drought could favor the most deep-rooted species in ecosystem. [Abstract from authors]

Dynamics of Fremont cottonwood (Populus fremontii) and saltcedar (Tamarix chinensis) populations along the San Pedro River, Arizona Abstract Woodlands of the exotic saltcedar (Tamarix chinensis) have replaced forests of native Fremont cottonwood (Populus fremontii) and willow (Salixspp.) along many rivers of the American South-west. In the middle basin of the San Pedro River, saltcedar dominates only at the drier sites where the surface and ground-water conditions no longer support cottonwood–willow forests. At sites with perennial (or near-perennial) stream flow, saltcedar is co-dominant with Fremont cottonwood. However, saltcedar has been declining in importance at these sites, perhaps due to recent occurrence of conditions that favour cottonwood establishment (frequent winter flooding, high rates of stream flow during spring, exclusion of livestock). This shift provides evidence of capacity for self-repair in degraded Sonoran riparian ecosystems. In the upper basin, in contrast, saltcedar has increased in relative abundance at sites that show evidence of ground-water decline, signaling a need for vigilance in river management. Saltcedar is generally sparse in the upper basin, probably due to the combination of cool temperatures and persistence of perennial or near-perennial stream flows in most areas. Throughout the San Pedro River, saltcedar and cottonwood both have been influenced by changing flood patterns. Expansion of Fremont cottonwood populations and initial colonization by saltcedar both correlate with post-1960 increases in fall and winter flood frequency and decreases in summer flood size. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WH9-45J55XG-T&_user=109269&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1090197180&_rerunOrigin=scholar.google&_acct=C000059546&_version=1&_urlVersion=0&_userid=109269&md5=e6386d13fa074e33400238658263d02d

Here's another interesting site about Tamarisk: Some examples of information? "Saltcedar’s success in riparian environments in the Southwest appears to be a function of its phenomenal reproductive output and its greater drought and flood tolerance, as compared to Salix exigua"

Abstract. Desertification of shrub and grassland into pinyon-juniper woodland is occurring over much of the Colorado Plateau in the southwestern United States. As trees invade, they out-compete shrubs and grasses, increasing erosion rates and reducing infiltration of moisture into the soil. This has caused habitat problems for wildlife, and reduced forage for livestock. These impacts also affect the human communities that rely on ranching and tourism related to hunting. Past land use and management practices including heavy livestock grazing, fire suppression and introduction of exotic annual plants are believed to have led to current conditions. The Montrose office of the Bureau of Land Management has implemented an ecosystem-based program to reverse the desertification process on public land. The program is centered on detailed landscape objectives describing the desired vegetation mosaic on 360 000 ha of public land. The objectives outline proportions of plant seral stages and arrays of patch sizes for each planning unit. These objectives are based on priority management issues and the need to replicate a natural vegetation mosaic. Where the existing mosaic does not meet objectives, mechanical vegetation treatments and prescribed fire are used to create early and mid-seral patches on the ground. This restored vegetation pattern and type should be sustained over time through a natural fire regime and improved livestock management. Because many uncertainties exist, an adaptive management process is being used that allows mosaic objectives to be changed or processes modified where monitoring or scientific research indicate a need.

Absract 1. Restoration of wildland fire to forests is a challenge when historical fire regimes have been altered. We studied four fires that burned over approximately 7865 ha on an altitudinal gradient in Grand Canyon National Park, USA, in 2003. The fires met criteria for the current USA policy allowing the restoration of fire's ecological role in forest landscapes: Wildland Fire Use for Resource Benefits. 2. After the fires burned out, we remeasured 82 permanent pre-established monitoring plots burned by the fires plus 43 additional plots on unburned companion sites. 3. The maximum height of charring of tree boles and basal area mortality increased in mean value and variability with altitude. At a low-altitude Pinus–Quercus site, tree density declined significantly but basal area was unchanged. At a mid-altitude mixed-conifer site and a high-altitude Picea/Abies/Populus site, both density and basal area declined. 4. The thinning effect of fire was concentrated on smaller, shorter, fire-susceptible trees. Small-diameter trees (< 20 cm diameter) made up 79–95% of all tree mortality. Shade-tolerant conifers, particularly true firs and spruce, experienced disproportionate mortality (31–82% basal area decline), while fire-resistant ponderosa pine and Douglas fir tended to survive (2–8% basal area decline). Delayed mortality between the first and second years following the fires accounted for only 4•2% of trees dying at the low-altitude site but 15•6% and 11•2% at the mid- and high-altitude sites, respectively. Regeneration density was highly variable but forest floor and woody debris declined in burned areas. 5. Synthesis and applications. This study shows that, even after an unusually long fire-free period (1880–2003), at the mid- and high-altitude burned sites fire effects were consistent with restoration of historical patterns, moving the ecosystems closer to historical reference conditions. Fires simultaneously reduced the living, dead and ladder fuels that made the forest vulnerable to uncharacteristically severe fire. These effects make the forests more resistant to the expected increases in fire size and severity under future climate conditions. Even at longer-than-historical fire intervals, the wildland fire use policy can benefit Grand Canyon forests.

Studies suggest an increase in winter rainfall for the Colorado Plateau over the next century. Although this could elevate water supplies, any benefits could also be offset — partially or entirely — by increased evaporative loss in water delivery systems and rising demand from a growing population. Average snowpack in the Colorado River basin may decrease by 30 percent by the middle of the next century. Runoff will peak earlier (by more than a month earlier). In addition, heavy winter rains may cause flooding, accelerate soil erosion, and pose greater risks to property and life.

The Colorado Plateau is located in the interior, dry end of two moisture trajectories coming from opposite directions, which have made this region a target for unusual climate fluctuations. A multi-decadal drought event some 850 years ago may have eliminated maize cultivation by the first human settlers of the Colorado Plateau, the Fremont and Anasazi people, and contributed to the abandonment of their settlements. Even today, ranching and farming are vulnerable to drought and struggle to persist. The recent use of the Colorado Plateau primarily as rangeland has made this region less tolerant to drought due to unprecedented levels of surface disturbances that destroy biological crusts, reduce soil carbon and nitrogen stocks, and increase rates of soil erosion. The most recent drought of 2002 demonstrated the vulnerability of the Colorado Plateau in its currently depleted state and the associated costs to the local economies. New climate predictions for the southwestern United States include the possibility of a long-term shift to warmer, more arid conditions, punctuated by megadroughts not seen since medieval times. It remains to be seen whether the present-day extractive industries, aided by external subsidies, can persist in a climate regime that apparently exceeded the adaptive capacities of the Colorado Plateau’s prehistoric agriculturalists.